Assessing the maximum size of annual foodborne outbreaks in the United States: An analysis of 1973–2016 outbreaks

Foodborne disease outbreaks are rare events that can be extremely costly in terms of public health as well as monetary losses for industry and government. These events can overwhelm the local public healthcare network and exceed the capacity of epidemiologists and local public health officials to investigate and manage the outbreak. Planning and allocation of sufficient resources requires an understanding of both the frequency and magnitude of large foodborne outbreaks. Describing these two characteristics is difficult because most statistical methods describe central tendencies of the phenomena under study. An exception is extreme value theory (EVT), which intends to estimate the size and frequency of adverse events as large as, or larger than, those previously observed. This study applies extreme value theory methods to foodborne disease outbreak data collected in the United States between 1973 and 2016. A brief summary of the data, including changes in the surveillance system and their effect on the outbreak data, is provided. Estimates of the outbreak size expected to be exceeded within time periods of 10, 20, 40 and 100 years, referred to as the return level, ranged from 2500 to 10,400. The estimated time period time between outbreaks (i.e., the return period) of at least 500, 5,000, 10,000 and 20,000 cases ranged from 1 to greater than 400 years.